Multichannel cochlear implant speech processing: further variations of the spectral maxima sound processor strategy

Abstract

The spectral maxima sound processor (SMSP) was first developed at the University of Melbourne in 1989. A full description of the SMSP has been given by McDermott et al.1 In short, the SMSP utilizes an ear-level microphone to measure acoustic sound pressure. A 16-channel band-pass filter bank is used to analyze the sound spectrum at discrete time intervals. Each of the 16 filters is assigned to one of the 16 intracochlear electrodes according to frequency. Within each time interval the six channels with the largest band-pass filter amplitudes are selected and used to stimulate six corresponding electrodes in quick succession. The current implementation of the SMSP2 differs from the original in that a digital signal processor is used in place of the analog filter bank and the microprocessor. The filter bank has been implemented with a discrete Fourier transform. Also, the input dynamic range has been improved by increasing the resolution of the analog-to-digital converter from 8 to 12 bits.